const hexcase = 0; /* hex output format. 0 - lowercase; 1 - uppercase */
const chrsz = 8; /* bits per input character. 8 - ASCII; 16 - Unicode */
export function hex_sha1(s) {
  return binb2hex(core_sha1(AlignSHA1(s)));
}

/*
 *
 * Convert an array of big-endian words to a hex string.
 *
 */
function binb2hex(binarray) {

  var hex_tab = hexcase ? '0123456789ABCDEF' : '0123456789abcdef';

  var str = '';

  for (var i = 0; i < binarray.length * 4; i++) {

    str += hex_tab.charAt((binarray[i >> 2] >> ((3 - i % 4) * 8 + 4)) & 0xF) +

      hex_tab.charAt((binarray[i >> 2] >> ((3 - i % 4) * 8)) & 0xF);

  }

  return str;

}

/*
 *
 * Calculate the SHA-1 of an array of big-endian words, and a bit length
 *
 */
function core_sha1(blockArray) {

  var x = blockArray; // append padding
  var w = Array(80);

  var a = 1732584193;

  var b = -271733879;

  var c = -1732584194;

  var d = 271733878;

  var e = -1009589776;

  for (var i = 0; i < x.length; i += 16) // 每次处理512位 16*32
  {

    var olda = a;

    var oldb = b;

    var oldc = c;

    var oldd = d;

    var olde = e;

    for (var j = 0; j < 80; j++) // 对每个512位进行80步操作
    {

      if (j < 16)
        w[j] = x[i + j];

      else
        w[j] = rol(w[j - 3] ^ w[j - 8] ^ w[j - 14] ^ w[j - 16], 1);

      var t = safe_add(safe_add(rol(a, 5), sha1_ft(j, b, c, d)), safe_add(safe_add(e, w[j]), sha1_kt(j)));

      e = d;

      d = c;

      c = rol(b, 30);

      b = a;

      a = t;

    }

    a = safe_add(a, olda);

    b = safe_add(b, oldb);

    c = safe_add(c, oldc);

    d = safe_add(d, oldd);

    e = safe_add(e, olde);

  }

  return new Array(a, b, c, d, e);

}

/*
 *
 * The standard SHA1 needs the input string to fit into a block
 *
 * This function align the input string to meet the requirement
 *
 */
function AlignSHA1(str) {

  var nblk = ((str.length + 8) >> 6) + 1, blks = new Array(nblk * 16);

  for (var i = 0; i < nblk * 16; i++)
    blks[i] = 0;

  for (i = 0; i < str.length; i++)

    blks[i >> 2] |= str.charCodeAt(i) << (24 - (i & 3) * 8);

  blks[i >> 2] |= 0x80 << (24 - (i & 3) * 8);

  blks[nblk * 16 - 1] = str.length * 8;

  return blks;

}

/*
 *
 * Perform the appropriate triplet combination function for the current
 * iteration
 *
 * 返回对应F函数的值
 *
 */
function sha1_ft(t, b, c, d) {

  if (t < 20)
    return (b & c) | ((~b) & d);

  if (t < 40)
    return b ^ c ^ d;

  if (t < 60)
    return (b & c) | (b & d) | (c & d);

  return b ^ c ^ d; // t<80
}

/*
 *
 * Determine the appropriate additive constant for the current iteration
 *
 * 返回对应的Kt值
 *
 */
function sha1_kt(t) {

  return (t < 20) ? 1518500249 : (t < 40) ? 1859775393 : (t < 60) ? -1894007588 : -899497514;

}

/*
 *
 * Add integers, wrapping at 2^32. This uses 16-bit operations internally
 *
 * to work around bugs in some JS interpreters.
 *
 * 将32位数拆成高16位和低16位分别进行相加，从而实现 MOD 2^32 的加法
 *
 */
function safe_add(x, y) {

  var lsw = (x & 0xFFFF) + (y & 0xFFFF);

  var msw = (x >> 16) + (y >> 16) + (lsw >> 16);

  return (msw << 16) | (lsw & 0xFFFF);

}

/*
 *
 * Bitwise rotate a 32-bit number to the left.
 *
 * 32位二进制数循环左移
 *
 */
function rol(num, cnt) {

  return (num << cnt) | (num >>> (32 - cnt));

}

/*
 *
 * Perform a simple self-test to see if the VM is working
 *
 */
function sha1_vm_test() {

  return hex_sha1('abc') == 'a9993e364706816aba3e25717850c26c9cd0d89d';

}

